Sometimes Wordfence locked out from the signing in our users..

Do you know which error messages they are getting?

Depending on the message, it could be some of the settings chosen on the Wordfence Options page, under the “Login Security Options” section, or “Firewall Rules.” If you can post a screenshot of your current options in those two sections, we can see which ones might be too strict.

Thanks for the additional details. If the username listed in the error message above is a valid user, then it probably is a conflict between plugins — from your screenshot, either the Oneall Social Login plugin you mentioned or possibly iThemes Security.

Turning off the Wordfence option “Immediately lock out invalid usernames” should let them log in again. If you like, you can enter common bad usernames, in the field below, “Immediately block the IP of users who try to sign in as these usernames”, to block most of the bad users, while still letting real users through.